No rear brakes problem... proportioning valve question

[Zone47]

My truck is a 68 C10 - drum/drum with no booster.

I thought the problem was the master cylinder, so I bought a new one today, gave it a good bench bleed and install, still no rears. There is no fluid at all out of the bleed screws in the rear. Could it be the proportioning or routing block?

I ohmed the switch (out of the bottom) to ground but it's not shorted. I removed it but it's just a flathead screw head on the inside with a couple of o-rings. I don't feel any notch on the inside. It's a very strange setup.

So it looks like the faults are either the proportioning valve, the rear flex line, or the wheel cylinders? Which sounds like the most likely culprit in this case?

This pic is with the old master cylinder>

[HO455]

I would suspect the hose. But before purchasing a hose I would have a friend help bleed the brakes.
Starting at the master cylinder work your way back. Verify you have fluid at each end of the proportioning valve. If that is good then check for fluid at the top of the hose moving to the bottom of the hose next. If fuild is good at the bottom of the hose it is time to crack the tubing fitting at the wheel cylinders.
As you work your way back inspect the entire length of the brake tubing for signs of leaking or crushed tubing.
The photos are of damaged brake lines on my Burban I discovered after bought it.

[Zone47]

Originally Posted by HO455

I would suspect the hose. But before purchasing a hose I would have a friend help bleed the brakes.
Starting at the master cylinder work your way back. Verify you have fluid at each end of the proportioning valve. If that is good then check for fluid at the top of the hose moving to the bottom of the hose next. If fuild is good at the bottom of the hose it is time to crack the tubing fitting at the wheel cylinders.
As you work your way back inspect the entire length of the brake tubing for signs of leaking or crushed tubing.
The photos are of damaged brake lines on my Burban I discovered after bought it.

It was the valve I was worried about but that's a good idea just working my way down the 'line' so to speak. Thanks!

[Zone47]

Update: It was the rear brake hose. It was completely blocked up. No fluid getting out after the hose. The passenger rear line was plugged as well but popped open during the bleed process.

Brakes are much better!!

Thanks for the help!

[HO455]

Congratulations! And thanks for the follow-up post. We all learn from them.